Naloxone and Nalmefene | Naltrexone
Opiate antagonists bind to opiate receptors, but they do not activate
the receptor to initiate the chain of cellular events that produce
so-called opiate effects. Naloxone is available as a parenteral
form that can be given subcutaneously, intramuscularly, or intravenously
to reverse opiate overdose. It can be used to reverse opiates used
in operative anesthesia or to treat overdoses in the emergency department.
The dosage depends on the amount of opiate taken and the potency
of the opiate. Overdoses from fentanyl, a highly potent opiate, require
large doses of naloxone given repeatedly until the patient's
breathing improves. Nalmefene is also available in a parenteral
form for reversal of overdose. The main difference is that nalmefene
has a much longer duration of action than naloxone. The effects
of naloxone can disappear in 20–30 minutes; therefore,
in cases of overdose, the patient needs to be monitored and either
given repeated doses of naloxone or given a continuous intravenous
drip. Naloxone is also useful in the diagnosis of physical dependence.
If the presence of physical dependence is in question, a small (0.2-
to 0.8-mg) injection of naloxone can be given. In a dependent individual,
an opiate withdrawal syndrome would occur immediately, but it would
be short lived (i.e., 20–40 minutes).